Among the various video display systems available in the art, an optical projection system is known to be capable of providing high quality images in a large scale.
In FIG. 1, there is illustrated a prior art optical projection system 100 comprising a light source 10, a source lens 20, a source stopper 22 provided with a light transmitting portion 26 and a light stopping portion 24, a total reflection mirror 30 including a reflective surface 32, a beam splitting means 40, a trinity of arrays of M.times.N actuated mirrors 50, a first, a second and a third arrays 52, 54, 56 of M.times.N actuated mirrors 50, a trinity of field lenses including a first, a second and a third field lenses 60, 62, 64, a projection stopper 70 provided with a light transmitting portion 74 and a light stopping portion 72, a projection lens 80 and a projection screen 90.
In such a system, a white light emanating from the light source 10 is focussed along a first optical light path onto the light transmitting portion 26 on the source stopper 22 by the source lens 20 located between the light source 10 and the source stopper 22, wherein the white light consists of a first, a second and a third primary colors. The source stopper 22 is used for shaping the white light from the light source 10 via the source lens 20 into a predetermined configuration by allowing a specific portion of the white light to pass through the light transmitting portion 26 thereof. The white light from the source stopper 22 travels onto the reflective surfaces 32 of the total reflection mirror 30 in a facing relationship with the source stopper 22 and the beam splitting means 40. The white light reflected from the reflective surface 32 of the total reflection mirror 30 travels along a second optical path, and is uniformly illuminated onto the beam splitting means 40 including the first and second dichroic mirrors 42, 44. The first dichroic mirror 42 disposed between the total reflection mirror 30 and the second dichroic mirror 44 facing the first array 52 of M.times.N actuated mirror 50, receives the white light from the reflective surface 32 of the total reflection mirror 30, isolates and reflects the first primary light beam of the white light to the first array 52 of the M.times.N actuated mirrors 50, and transmits the second and third primary light beams to the second dichroic mirror 44. The second dichroic mirror 44 disposed between the third array 56 of M.times.N actuated mirror 50 and the first dichroic mirror 42 facing the first array 52 of M.times.N actuated mirror 50, upon receiving the second and third primary light beams from the first dichroic mirror 42, isolates and reflects the second primary light beam to the second array 54 of the M.times.N actuated mirrors 50, and transmits the third primary light beams to the third array 56 of M.times.N actuated mirrors 50. Each of the actuated mirrors 50 in the array 52, 54, 56 includes a mirror and an actuator made of a piezoelectric material or an electrostrictive material which deforms in response to an electric field applied thereto. Each of the actuated mirrors 50 in the arrays 52, 54, 56 corresponds to each of the pixels to be displayed.
Each of the first, second and third field lenses 60, 62, 64, located between the first dichroic mirror 42 and the first array 52 of M.times.N actuated mirrors 50, the second dichroic mirror 44 and the second array 54 of M.times.N actuated mirrors 50, and the second dichroic mirror 44 and the third array 56 of M.times.N actuated mirrors 50, respectively, is used for collimating each of the primary light beams from each of the dichroic mirrors 42, 44 in the beam splitting means 40 to thereby uniformly illuminate each of the primary light beams onto the corresponding array of M.times.N actuated mirrors.
The reflected primary light beams from each of the undeflected actuated mirrors in each of the arrays 52, 54, 56 are focussed back to the projection stopper 70 by the corresponding field lens via the beam splitting means 40 through the light transmitting portion 74 of the projection stopper 70, whereas the reflected primary light beams from each of the deflected actuated mirrors in each of the arrays 52, 54, 56 are focussed back to the projection stopper 70 by the corresponding field lens via the total reflection mirror 30 and partially stopped by the light stopping portion 72 of the projection stopper 70 so that a portion of the focussed primary light beams passes through the light transmitting portion 74 to thereby modulate the intensity of the primary light beams. The primary light beams from each of the actuated mirrors 50 in the arrays 52, 54, 56 which pass through the light transmitting portion 74 of the projection stopper 70 located at the focal point of the field lenses 60, 62, 64 are transmitted to the projection lens 80 which, in turn, projects the transmitted primary light beams onto the projection screen 90.
One of the major shortcomings of the above-described optical projection system 100 is the size thereof, arising from the use of the pair of dichroic mirrors 42, 44, which, in turn, necessitates the use of the trinity of arrays 52, 54, 56 of M.times.N actuated mirrors 50 and the field lenses 60, 62, 64, thereby making the optical projection system 100 bulky and structurally complicated.